Pollinator limitation and inbreeding depression in orchid species with and without nectar rewards

Abstract

• Many orchids produce no nectar rewards. Foraging pollinators should visit more flowers per inflorescence in species with nectar, which could increase geitonogamous self-fertilization. If a history of selfing decreases genetic load, then nectar-producing orchids should harbour lower inbreeding depression than nectarless species. • Here, I tested this hypothesis by quantifying inbreeding depression and pollinator limitation in populations of three closely related orchid species, one of which provides nectar. I also compared inbreeding depression for nectarless and nectar-producing species of orchids using published studies. • All field populations expressed pollinator limitation, but the nectar-providing species was intermediate to the two nectarless species. All populations expressed inbreeding depression, and levels increased in later life-history stages. There was no tendency for nectarless species to express higher inbreeding depression either in experiments or published studies. • Nectarless orchids may not express higher levels of inbreeding depression because pollinators fail to visit more flowers in nectar-bearing species, because such visitations do not result in greater selfing, and/or because higher selfing may be ineffective in purging the mutations that cause load. © The Authors (2005).